Interpretive Summary: The ability of two species of insect-pathogenic nematodes, Steinernema carpocapsae (Weiser) and Steinernema feltiae (Filipjev) to control navel orangeworm (Amyelois transitella (Walker)) in almond and pistachio nuts on the ground was investigated in this study. S. carpocapsae applied to 1-m2 plots by backpack sprayer at a water application rate of 3,740 l/ha and a concentration of 10 infective juveniles (IJs)/cm2 produced 89 and 96% larval mortality in pistachios and almonds, respectively. In contrast, when S. feltiae was applied at the same concentration and water rate, it caused lower mortality (74.0 and 78.9%, respectively). This disparity may be related to formulation differences because S. carpocapsae was laboratory-reared and S. feltiae was commercially produced. When commercial formulations of both EPNs were applied to almonds in 0.2 ha plots, using a tractor-pulled herbicide sprayer and a water application rate of 1,870 l/ha and a concentration of 50 IJs/cm2, the mortality produced by S. carpocapsae and S. feltiae was comparable. S. carpocapsae was more effective against larvae in almonds that were half buried than almonds on the surface (88.2%, 66.2% mortality, respectively) while almond burial had no effect on S. feltiae (76.0% mortality). This study demonstrated that EPNs can play a role in post harvest sanitation, but further research is necessary to determine if lower, more economical concentrations of both nematodes and application rates can provide similar control.

Technical Abstract:
The ability of two species of entomopathogenic nematodes (EPNs), Steinernema carpocapsae (Weiser) and Steinernema feltiae (Filipjev) to control navel orangeworm (Amyelois transitella (Walker)) in almond and pistachio nuts on the ground was investigated in this study. S. carpocapsae applied to 1-m2 plots by backpack sprayer at a water application rate of 3,740 l/ha and a concentration of 10 infective juveniles (IJs)/cm2 produced 89 and 96% larval mortality in pistachios and almonds, respectively. In contrast, S. feltiae IJs applied at the same concentration and water rate caused 74.0 and 78.9% mortality, respectively. The difference between the two species was significant, but may be related to formulation differences because S. carpocapsae was laboratory-reared and S. feltiae was commercially produced. Commercial formulations of both EPNs were also applied to almonds in 0.2 ha plots, using a tractor-pulled herbicide sprayer and a water application rate of 1,870 l/ha and a concentration of 50 IJs/cm2. The mortality produced by S. carpocapsae and S. feltiae was comparable in this experiment, although S. carpocapsae was more effective against larvae in almonds that were half buried than almonds on the surface (88.2%, 66.2% mortality, respectively) while almond burial had no effect on S. feltiae (76.0% mortality). S. feltiae persisted longer than S. carpocapsae, 12 and six weeks, respectively. This study demonstrated that EPNs can play a role in post harvest sanitation, but further research is necessary to determine if lower, more economical concentrations of both nematodes and application rates can provide similar control.